1. Field of the Invention
The present invention relates to a covered member which is formed by covering a base material such as irons and steels with a hard film and which is improved in bond strength of the base material and the covering film, and to a method of producing the same.
2. Description of the Background
Widely used is a covered member which is produced by forming a metallic film, a ceramic film, a carbon-base film, or the like of several to tens of microns in thickness on a surface of irons, steels or the like by physical vapor deposition (PVD) or chemical vapor deposition (CVD), and which comprises the base material, and the covering film covering a surface of this base material. The bond strength of the base material and the covering film, which constitute this covered member, becomes a problem and in some cases the film is peeled off. For example, in the art of employing PVD and applying a hard film to a base material which has a low temperature of 600.degree. C. or less, the bond strength of the base material and the covering film is small because of low temperature, and the film is often peeled off.
In such a case, as means of increasing the bond strength of the base material and the covering film, there have so far been employed a method of cleaning a base material surface by sputtering the base material surface, a method of roughening a base material surface by blasting the base material surface, and so on.
In using a covered member as a sliding member, it is important that its covering film is smooth and bond strength of the covering film and a base material is high. When the covering film is not smooth, seizure resistance is low and a tendency to attack a mating member is increasing. When the bond strength of the covering film and the base material is insufficient, the film is peeled off and the covered member cannot be used as a sliding member.
However, in the sputtering method, although organic stains and oxides can be removed from the surface, it is often that a desired bond strength is not obtained in the case of low temperature film application. In the blasting method, the base material surface is greatly roughened into an uneven surface with projections and concaves of about several microns at the minimum, so a smooth film cannot be obtained. Hence, the surface roughness of a hard film thereafter formed deteriorates. For instance, when used as a sliding member, the covered member rather abrades a mating member and desired sliding characteristics cannot be obtained. Accordingly, when the covered member is used, for example, as a sliding member which needs to have a smooth surface, repolishing of the hard film is sometimes required.